Of late, there has been developed a retainer type sealed lead storage battery which has no leakage of water and no need for supplemental water so as to have no maintenance. Such a sealed lead storage battery comprises porous separators between adjacent plates and electrolyte filled in the case so as to be retained at least in the porous separators. The porous separators may be formed of glass fine fiber mat, for example. In this sealed lead storage battery, it is considered that oxygen gases generated at positive plates are reduced at three interfaces of oxygen gases, lead of negative plates and electrolyte to be returned to water as expressed by the following formula: EQU 2Pb+O.sub.2 +2H.sub.2 SO.sub.4 .fwdarw.2PbSO.sub.4 +2H.sub.2 O
When the battery is over-charged, the oxygen gases are absorbed at the negative plates where there occurs reduction of lead sulfate (PbSO.sub.4). This prevents hydrogen gases from being generated, which enables the storage battery to be sealed.
However, this sealed lead storage battery consumes the remaining fluid electrolyte so that an amount of electrolyte is necessarily reduced. Thus, reduction of electrolyte on trickle charge causes the storage battery to have a shortened life.
In order to avoid such a drawback, it is required to increase an amount of electrolyte. However, it is also required that electrolyte has to be fixed without change in a volume of the whole storage battery for provision of compactness and no leakage of solution. Since the sealed lead storage battery has most electrolyte retained in glass fine fiber mats and porous active materials of the plates, the volume of the whole storage battery has to be essentially increased in order to retain more electrolyte.
Furthermore, a capacity of the sealed lead storage battery relies on closeness of the plates to the retainer. If the plates are poorly close to the retainer, then the plates cannot communicate with the electrolyte, which deteriorates the efficiency of the storage battery. This is caused by decrease in the capacity of discharge which is in turn caused by decrease in amount of solution due to generation of gases which is caused by decomposition of water on trickle of floating charge or due to evaporation of electrolyte on use at relatively high temperature.
In case the electrolyte is formed of gel mainly comprising powder of sodium sulfate, sulfic acid and silicon oxide, the storage battery is deteriorated by removing water out of the gel layer to generate isolated water, contracting the gel layer due to its hardness, separating the surfaces of the plates from the gel layer, preventing charging reaction with the plates and lowering the capacity of the storage battery, which provides a shortened life to the storage battery.